Adamant Golem

Tough. When an enemy does more than 400 damage, it is reduced to 400

Smash Melee Weapon Attack: +20 to hit, reach 5 ft., one target. Hit:  4d10 + 10 bludgeoning damage. 

Stomp. Melee Weapon Attack: +16 to hit, reach 10 ft., all targets. Hit: 8d10 + 20 Bludgeoning damage. 

Shove. Melee Weapon Attack: +19 to hit, reach 5 ft., 1 target. Hit: 3d10 + 5 bludgeoning damage. Shoves the target back 30 ft

This Golem has 4 legendary actions and regains spent actions on the end of it's turn 

 Smash, Make one smash attack

Pummel, (Costs 3 Actions) Make 4 smash attacks

Shove, makes 1 shove action

Indestructible(costs 4 actions) until the start of it's next turn it is immune to all damage(you can't use more legendary actions for 4 turns)

Stomp (costs 2 actions) make 1 stomp attack